Improvements for use with tissue expanders are provided. A tissue expander includes: a selectively inflatable and deflatable shell that is configured to be implanted; and an access port for selectively inflating and deflating the shell, the access port comprising a sidewall, a base at a first end, and a membrane at a second end opposite the first end, wherein the sidewall and the base of the access port are constructed of a material that is non-reactive with a magnetic resonance imaging (MRI) machine. In embodiments, the tissue expander includes a magnet at the access port. In embodiments, the magnet is configured with a physical size and magnetic force such that, when the tissue expander is implanted, the magnet is detectable by an external magnetometer sensor but is not detectable by an external dangle-magnet.